I have been keeping my CFI certs current but haven't instructed in a few years, as I fly 135 for a living. An acquaintance who has his PPL and his own airplane has asked to receive instrument instruction. Am I required to verify and document his citizenship before he can log dual received? He is a US citizen. Are there any other paperwork gotchas that I need to be aware of? I'm sure I knew all of this at one time....

If he doesn't have the endorsement in his logbook, you are required to check his citizenship status for PPL/Multi/IR instruction.

Actually, even if he has the endorsement from another instructor if he is a first-time student for you you're required to document it in your records (a photocopy of the passport) as well as give him another endorsement in the logbook. And if it's a primary student you get to assist with getting the student a student pilot certificate! All so the TSA can vet student pilots and you can vet them, too!

Yay TSA